Rat pups are given intraperitoneal injections containing various concentrations of fluoride and radiolabeled 45 Ca on days of age 5, 9 and 15-20. The animals are sacrificed just prior to eruption of first molars, the jaws resected and the teeth examined for radioactivity. A group of rat pups treated in the same manner using non-radioactive Ca are used to study the development of dental caries.